Lidar is a radar-like system that uses lasers to create three-dimensional representations of surrounding environments. A Lidar unit includes at least one laser emitter paired with a detector to form a channel, though an array of channels may be used to expand the field of view of the Lidar unit. During operation, each channel emits a laser signal into the environment that is reflected off of the surrounding environment back to the detector. A single channel provides a single point of ranging information. Collectively, channels are combined to create a point cloud that corresponds to a three-dimensional representation of the surrounding environment. The Lidar unit also includes circuitry to measure the time of flight—i.e., the elapsed time from emitting the laser signal to detecting the return signal. The time of flight is used to determine the distance of the Lidar unit to the detected object.
Some Lidar units also measure the intensity of the return signal. The intensity of the return signal provides information about the reflectance of the surface reflecting the signal and can be used for object detection. The intensity of the return signal depends on a number of factors, such as the distance of the Lidar unit to the detected object, the angle of incidence of the emitted laser signal, the temperature of the surrounding environment, and the actual reflectance of the detected object. Other factors, such as the alignment of the emitter and detector pairs, add signal noise that may further impact the uniformity of intensity values output by each channel.
Increasingly, Lidar is finding applications in autonomous vehicles (AVs) such as partially or fully autonomous cars. Frequently, the intensity values returned by each Lidar channel are used in the localization, perception, prediction, and motion planning of AVs because these signals provide information related to the reflectance of detected objects. However, given the lack of uniformity of Lidar intensity values caused by signal noise and the other factors that impact intensity of return signals described above, use of the raw intensity values provided by the Lidar unit often leads to inaccuracies and other problems with localization, perception, prediction, and motion planning for autonomous and semi-autonomous vehicles.